Electrically conducting coating on



Reissuecl Sept. 30, 1952 UNITED STATES ELECTRIC ALLY CONDUCTING COATING ON GLASS AND OTHER CERAMIC BODIES John M. Mochel, Louisville, Ky., assignor to Corning Glass Works, Corning, N. Y., a corporation of New York N Drawing.

Original No. 2,564,709, dated August 21, 1951, Serial No. 197,515, November 24, 1950. Application for reissue May 15, 1952, Se-

rial No. 288,010

1 Claim.

Matter enclosed in heavy brackets II appears in the original patent but forms no part of thi reissue specification; matter printed in italics indicates the additions made by reissue.

This application, which is a continuation-1m part of my pending application Serial Number 771,859 filed September 3, 1947, now Patent No. 2,564,707 issued August 21, 1951, relates to electric resistance devices and is particularly directed to such a device comprising a glass or other nonporous vitreous ceramic surface provided with an electrically conducting iridized metal oxide film.

Electrically conducting metal oxide films produced by iridization of glass or other vitreous ceramic surfaces have recently been found useful as the resistance elements in electric resistance devices variously adapted for heating and other purposes.

Among the metal oxides which have been proposed for such application is tin oxide, the iridized films of which possess sufficiently low resistances to make their use as electric resistance elements especially attractive. Such films are, however, subject to easy poisoning" in that the presence of a small amount of another metal oxide such as cadmium oxide, chromium oxide, copper oxide, iron oxide, zinc oxide, and the like effects such an increase in resistance that the films may be rendered practicall useless for heating purposes. Presumably, with the excel tion of 0010, which has a lower resistance, this efiect is due to the higher resistance exhibited by each of such other oxides in its corresponding iridized form. The eflect of CdO in so raisi the resistance of tin oxide films cannot be crcplained.

As disclosed in my pending application Serial Number 771,860 filed September 3, 1947, now Patent No. 2,564,987, issued August 21, 1951, iridized films of indium oxide are also electrically conducting and are useful as electric resistance elements. Such a film, however, has a considerably higher resistance than an iridized tin oxide film of corresponding thickness.

I have now discovered that, despite such higher resistance, indium oxide can be combined with tin oxide in iridized form to produce films having resistances not only lower than those of corresponding indium oxide films but unexpectedly also lower than those of corresponding tin oxide films. Such lower resistance films, which find particular application as the resistance elements in electric heating devices and the like, comprise primarily indium oxide and tin oxide equiv alent to approximately 0.1% to 45% Shoe. A further advantage of these films is that varying amounts of other metal oxides such as those that normally poison a film of tin oxide alone can be tolerated without any substantial adverse effect On their resistances.

The present films can be produced in the same manner as corresponding films of indium oxide or tin oxide alone. The glass or other vitreous ceramic surface to be iridized is heated to an elevated temperature of on the order of about 650 C. and preferably about 700 C.; and a so-- lution containing a compound of indium and a so is generally sufficient, a 10 to 20 second treatment ordinarily producing a film of the third or fourth order of thickness.

(The thickness of such a film may be gauged by the apparent color caused by the interference of light waves reflected therefrom. As the thick ness of the film increases, its apparent color changes, and the order or succession of the colors with increasing thickness corresponds to that of the well-known Newton rings described at page 147 in A Treatise on Light" by R. A. Houstoun (Longmans Green 8: Co. Ltd., (1938) The respective color sequence for each order and the thickness in Angstroms, based on red because it distinguishes the successive orders, are as follows:

Although other compounds of indium or tin may be used, the respective chlorides are preferred on account of their availability. Of the various chlorides of tin, the pentahydrate of stannic chloride, SnCh-SI-LO, is preferable because it is an easily weighable crystalline sub- Aqueous solutions of such chlorides stance.

should contain suflicient free hydrochloric acid to prevent premature hydrolysis of the salts.

The resulting iridized glass or other ceramic surface is then provided with spaced terminals or electrodes for passage of an electric current through the film as by depositing a conventional silver metallizing paste along two opposite edges of the film and firing the same. Other means for introduction of the electric current into the film may of course be utilized for adaptation of the iridized surface as the resistance element in an electric resistance device.

The following examples are illustrative of the lowered resistances characteristic of the present films:

Examples 1 to 7 Percent Sn 01 Percent Ohms per 111203 Example square ow-qoc-cogrozo p -swe p RIC By way of contrast, an iridized tin oxide film of the fourth order of thickness has a resistance of about 200 ohms per square, and an iridized indium oxide film of the same thickness has a resistance of about 500 ohms per square.

(The electrical resistance of an iridized film is conveniently expressed in ohms per square for a stated thickness, the resistance of a square film being independent of the size of the square. The resistance, as will be understood, varies inversely with the thickness of the film.)

The presence of a. small amount of another metal oxide in the instant films does not appear to adversely affect their resistances to any substantial degree and, in fact, may serve to further lower their resistances in certain cases. The following examples are illustrative:

Example 8 A third order film produced from a solution consisting of 5.08 g. InCla, 0.28 g. SnCl4-5H2O, 0.21 g. CdC12-2H2O, 8 cc. H20 and 2 cc. 37% aqueous HCl, equivalent to 93% R1203, 3.5% SnOz and 3.5% CdO on the oxide basis, has a resistance of 55 ohms per square. In comparison, a fourth order film consisting of $1102 and 3.2% CdO has a resistance of about600,000 ohms per square.

Example 9 .A. third order film produced from a solution consisting of 5.08 g. InCla, 0.28 g. SnC14'5I-I2O, 0.85 g. FeC13-6H2O,.8 cc. H20 and 2 cc. 37% aqueous HCl, equivalent to 39.5% InzOs, 3.4% SIlOa and 7.1% F6203 on the oxide basis, has a resistance of 4'? ohms per square. In comparison, a fourth order film consisting of shoe and 3% of FezOz has a resistance of about 130,000 ohms per square.

Example 11 A third order film produced from a solution consisting of 5.08 g. InCla, 0.28 g. SnCll-5HzO, 0.053 g. ClOs, 8 cc. H20 and 2 cc. 37% aqueous HCl, equivalent to 95.1% 111203, 3.7% SnOz and 1.2% CrzOa on the oxide basis, has a resistance of 96 ohms per square. In comparison, a fourth order film consisting of $1102 and 4.3% C12O3 has a resistance of about 280,000 ohms per square.

I claim:

An electric resistance device comprising a non porous vitreous ceramic body having on a surface thereof an electrically conducting iridiaed metal oxide film integrally united with the surface and comprising primarily an oxide of indium and an oxide of tin equivalent to approximately 0.1% to 45% SnOz, said body being provided with spaced terminals in electrical contact with such film.

JOHN M. MOCHEL.

No references cited. 

